A recessive insertional mutation, caused by the integration of the transgene in our Tg737 line of transgenic mice, causes bilateral polycystic kidney disease (PKD) in all of the animals homozygous for the transgene; this animal may represent an animal model for inherited human recessive PKD. The transgene was used as a "molecular tag" initially to gain molecular access to the mutant locus. Portions of overlapping clones will be used on Southern blots to identify likely coding regions in the cloned genomic DNA flanking the transgene insertion site on the basis of evolutionarily-conserved sequences. Regions of homology between mouse and human cross-hybridizing fragments will be identified (likely exons) to generate a probe to study temporal and spatial expression using RNase protection assays. Northern blot studies will then provide information about size and abundance of transcripts, as well as the possibility that alternatively-processed forms exist. A full-length cDNA will be obtained by screening the appropriate developmental stage cDNA library with the same probe. The cDNA clone will be used to determine the intron/exon structure of the Tg737. Additionally, the cDNA will be utilized in in situ hybridization studies to more specifically determine where the Tg737 gene is normally expressed. The isolation of a full-length murine cDNA will permit the subsequent isolation of any homologous gene by virtue of conserved DNA regions. The characterization of the identified human gene will be initiated, and probes made available to interested clinical genetics.